[Clayart] loading kilns, again

[mel jacobson]

When propane hit 6 bucks a gallon a few years back many
potters lost money, or had to stop firing, and then they
lost customers.

Nils and I talked a great deal about pre/warming kilns over night.
It led to the realization that hot bricks, fired over night did not
have any insulation quality left.  The heat blew right threw them.

Warming a kiln for an hour or so before you turn the kiln to high is
prudent. You heat your shelves and furniture, melt wax off and get the
pots to 400F or so...Then hit burners. In a fuel kiln, you find the sweet
spot that keeps the temp going up, no stall.  If you take hours off your
firing, you start to make money and it is good for the Earth.

Nils did a great deal of study about "turbulence" or, getting the gases and
flame flying around in the kiln, no heat stuck at the bottom or the back, whatever.

At the time he was in touch with a large porcelain company that made thousands
of dishes a day. They used gas car kilns.  The engineers determined the cost of
production by weight. Take the total weight of what goes into a kiln, shelves,
pots whatever and calculate the time it takes to fire the kiln.  What Nils learned
was a well organized load with room in the kiln to create turbulence fired much
faster and saved energy. So,  by firing less weight, leaving spaces it saved money
and time.  (also, overloaded kilns fired with fuel often leave you with a dozen or
so pots that you must throw out. I save those pots for the next firing and then
I can fire for 100% quality pots.

Facts from a few days ago. Colleen has gobs of pots ready for Holiday Sales. So, she
came up the farm and we fired both stoneware kilns at the same time. She left room
in loading and organized the kiln to have a good spacing of shelves' or stagger.

The propane tank was at 70%. The small kiln fired in four hours during rain but no
wind, cone 10 over.) The tank used 1%. The big stoneware kiln fired in six hours. (it used to take
9 hours.) She did not over pack the kiln. Left space both horizontal and vertical.
Every pot fired was perfect. (I mean it, they were just as expected, not one pot had
to be thrown out or be a second, and if you know Colleen she is fussy perfect.)

Both kilns were warmed with a small burner for one hour before we turned on the big burners.
The kilns were at about 450F.  Colleen controlled the firings, and turned them off by her
standard. Works fine.

So, in review. Bricks are mostly k26. mixed with 23's. They kept the heat in the kiln.
The outside of the kiln could be touched with the bare hand at time of finish.
Spacing of pots was controlled. Lots of space for gas and flame to create turbulence.
90% of the firing was a controlled "sweet spot" amount of pressure. WE could have
easily doubled the pressure. We did not change the pressure at all during the firing.
In other words, it fired itself. The Pete's red was brilliant. A 3-5 inch rolling flame
from the peep starting at 1750  She moved the damper in about an inch.

We do not ever brag, we pass information that we find important. I have spent many years
trying to get it right, then pass on the information...Do what you want with the information,
it is up to you.  Why not down fire your electric kiln next time for four hours. See what
happens. Fire a half cone hotter next time.

And, please remember, long bisque firing, pots can touch, stack them, whatever, but long
firing and make perfect bisque...And, remember, an electric kiln needs space for the
heat to move. And every time potters tell me that their electric fires a cone
hotter at the bottom at the Art Center, and ruins everything...I look to the sky for the moon.
They give gold stars to the person that can cram the most pots into a firing. Nice.
mel

website: www.melpots.com
www.melpots.com/CLAYART.HTML